Growth and Spectral Response of <i>Lactuca sativa</i> L. to Soil Contamination with Microplastic

Abstract We studied the effect of soil contamination with microplastics on biomass accumulation and spectral response of Lactuca sativa L. grown on under stress conditions of heavy metal presence in the soil. Therefore, we quantified the impact of soil zinc content on the plant growth rate and spectral characteristics to understand whether the lettuce responses to heavy metal are affected by soil microplastic. The main method used in the study was the recording of leaf spectral index in the range from 400 to 1000 nm of lettuce plants grown on soil substrates with microplastics added with the rates of 0, 0.01, 0.03 or 0.1%. To assess the modifying effect of heavy metal on the spectral characteristics of plants, zinc salt was preliminarily added to the soil with the rates of 0 or 1000 mg/kg. Physiological responses to microplastics were pronounced for plants grown on both Zn-rich and Zn-free soils. Microplastics had a negative impact on biomass accumulation in the above-ground parts of plants, regardless of their content, as well as on zinc levels in the soil. Under the highest microplastic concentration studied, leaf reflectance increased significantly across the visible spectrum. Using lettuce plants as an example, the impact of soil contamination with microplastics on agricultural crops was assessed, and the possibility of using the spectroscopy method to determine the physiological state of plants was studied. The results can be useful for finding new ways to manage soil fertility, especially polluted ones, to increase the yield and quality of agricultural crops.